1. Field of the Invention
This invention relates to highly uniform woven fibrous structures formed from tapes of woven fabric, tapes of non-woven fabrics, or tapes of non-woven, unidirectionally oriented fiber arrays, as well as processes for their fabrication.
2. Description of the Related Art
Ballistic resistant articles fabricated from composites comprising high strength synthetic fibers are well known. Articles such as bullet resistant vests, helmets, vehicle panels and structural members of military equipment are typically made from fabrics comprising high strength fibers such as SPECTRA® polyethylene fibers or aramid fibers such as KEVLAR® and TWARON®. For many applications, such as vests or parts of vests, the fibers may be used in a woven or knitted fabric. For other applications, the fibers may be encapsulated or embedded in a polymeric matrix material and formed into non-woven fabrics. For example, in one common non-woven fabric structure, a plurality of unidirectionally oriented fibers are arranged in a generally co-planar relationship and coated with a matrix material to bind the fibers together. Typically, multiple plies of such unidirectionally oriented fibers are merged into a multi-ply composite. See, for example, U.S. Pat. Nos. 4,403,012, 4,457,985, 4,613,535, 4,623,574, 4,650,710, 4,737,402, 4,748,064, 5,552,208, 5,587,230, 6,642,159, 6,841,492, 6,846,758, all of which are incorporated herein by reference, which describe ballistic resistant composites including multiple plies of non-woven fiber plies.
To maximize ballistic resistance of fibrous ballistic resistant composite articles, it is desired for there to be minimal space between adjacent fibers to facilitate maximum engagement of the fibers with a projectile impact. One way to accomplish this is by incorporating more fibers or fiber layers within a composite. However, increasing fiber content makes the armor heaver, which is undesirable. Another way to achieve a minimum of space between fibers, particularly when fabricating non-woven materials from parallel fibers, is to spread out the fibers or their component filaments so that fewer fibers lie on top of each other. This allows a greater number of fiber layers or unidirectional fiber plies to be stacked on top of each other without altering the expected composite thickness, which enhances fiber engagement with projectile threats without increasing fabric weight.
When spreading fibers, however, it remains difficult to eliminate all fiber overlap in a single unidirectional fiber array, especially when spreading continuous fibers. Additionally, when arranging fibers into parallel arrays, with or without the aid of fiber spreading, it is difficult to maintain fiber uniformity across the entire width of the array, particularly when orienting long continuous fibers. Unidirectional arrays of fibers are typically processed as continuous fiber webs that are several kilometers in length and several centimeters wide. The substantial length of the fibers makes it difficult to maintain uniform fiber orientation along the entire width of the array during processing. This is problematic, because fiber non-uniformity in an array leads to uneven and unpredictable ballistic performance. In addition, processing large fiber webs requires the use of expensive equipment, which can be prohibitive for composite manufacture on a commercial scale.
It would be desirable to provide fibrous composites having reduced thickness and improved fiber uniformity, which may result in greater engagement with projectiles and improved ballistic resistance properties. It would also be desirable to provide a method for producing such composites that allows the use of less expensive processing equipment. The invention provides a solution to each of these needs.